1. Field of the Invention
This invention relates in general to fluid pressure control systems, and in particular to a braking apparatus having an antiskid control capability for use in automotive vehicles.
2. Technological Background
The brake fluid control apparatuses for conventional antiskid controllers for preventing locking of the wheels include a master cylinder provided with a fluid pressure generator, wheel cylinders, a reservoir and a pump, in which the intercommunication flow of the brake fluid between the various components are controlled with valves and normally closed valves. Some of these apparatuses are designed to prevent the transmission of fluid pulsations, produced by the pumping action during the antiskid operation, which are transmitted back to the fluid pressure generator (causing pedal kickbacks), for example, as disclosed in a U.S. patent application Ser. No. 904,988 by the present inventors.
The four wheeled vehicles which use such antiskid apparatus are normally provided with a dual brakeline system: a cross (X) line system and a front-back line system. In the X line system, the left front wheel cylinder and the right rear wheel cylinder are on a common line, and the right front wheel cylinder and the left rear wheel cylinder are on a common line. In the front-back line system, the front two wheels are on a common line and the rear two wheels are on another common line. With such dual line systems, even if one brakeline fails, it is possible to control the vehicle by the remaining sound brakeline. Adapting an antiskid apparatus on vehicles having a dual brakeline system is costly, because it is necessary to provide one flow valve and one normally-closed (n/c) valve for each wheel cylinder. However, it is possible to economize by using a common pump in a fluid circuit which is connected to one fluid pressure generation source of a master cylinder.
When an antiskid apparatus sharing a reservoir and a pump in one line is activated, it is possible to prevent the pressure pulsations to be transmitted back to the pressure generation source through the flow valve which is in the antiskid operation mode. However, the pressure pulsations can still feedback to the pressure generation source through the flow valve in the fluid circuit which is not in the antiskid operation mode, because the flow valve which communicates the pressure generation source with the discharge fluid circuit of the pump has a large fluid passage, and the pressure pulsations can be transmitted through the large passage back to the pressure generation source, thus causing unpleasant pedal kickbacks at the pressure generation source.